The present disclosure relates to vehicle drive systems. More particularly, the present disclosure relates to hybrid vehicle drive systems employing electric and hydraulic components.
Hybrid vehicle drive systems commonly employ at least two prime movers arranged in different configurations relative to a transmission. One known configuration is found in so-called “series-parallel” hybrids. “Series-parallel” hybrids are arranged such that multiple prime movers can power the drive shaft alone or in conjunction with one another.
In one known hybrid vehicle drive system, a first and second prime mover (e.g., an internal combustion engine and an electric motor/generator) are arranged in a parallel configuration and used to provide power to a drive shaft and a power take-off (PTO) shaft through a transmission. PTO shafts are generally used to drive auxiliary systems, accessories, or other machinery (e.g., pumps, mixers, barrels, winches, blowers, etc.). One limitation of this system is that the second prime mover is typically positioned between the first prime mover and the transmission, creating the need to reposition existing drive train components.
In another known hybrid vehicle drive system, a first prime mover (e.g., an internal combustion engine) drives a PTO through a transmission. A second prime mover (e.g., electric motor/generator) has been coupled directly to the PTO. One limitation of this system is that while it allows the electric motor to provide power to a drive shaft through the PTO, it does not provide power to a hydraulic pump for operation of vehicle mounted hydraulic components and equipment. The system also does not use a hydraulic motor/pump as the second prime mover. The system also does not allow a hydraulic motor/pump to be driven by either the internal combustion engine or by the electric motor/generator, nor does it allow the hydraulic motor/pump and electric motor/generator to be simultaneously driven by the engine. The system also does not use the hydraulic motor/pump and electric motor/generator to simultaneously provide power to a drive shaft.
Hybrid systems used in larger trucks, greater than class 4, have typically utilized two basic design configurations—a series design or a parallel design. Series design configurations typically use an internal combustion engine (heat engine) or fuel cell with a generator to produce electricity for both the battery pack and the electric motor. There is typically no direct mechanical power connection between the internal combustion engine or fuel cell (hybrid power unit) and the wheels in an electric series design. Series design hybrids often have the benefit of having a no-idle system, including an engine-driven generator that enables optimum performance, lacking a transmission (on some models), and accommodating a variety of options for mounting the engine and other components. However, series design hybrids also generally include a larger, heavier battery; have a greater demand on the engine to maintain the battery charge; and include inefficiencies due to the multiple energy conversions. Parallel design configurations have a direct mechanical connection between the internal combustion engine or fuel cell (hybrid power unit) and the wheels in addition to an electric or hydraulic motor to drive the wheels. Parallel design hybrids have the benefit of being capable of increased power due to simultaneous use of the engine and electric motor, having a smaller engine with improved fuel economy while avoiding compromised acceleration power, and increasing efficiency by having minimal reduction or conversion or power when the internal combustion engine is directly coupled to the driveshaft. However, parallel design hybrids typically lack a no-idle system and may have non-optimal engine operation (e.g., low rpm or high transient loads) under certain circumstances. Existing systems on trucks of class 4 or higher have traditionally not had a system that combines the benefits of a series system and a parallel system.
Therefore, a need exists for a hybrid vehicle drive system and method of operating a hybrid vehicle drive system that allows a drive shaft to receive power from at least three components. There is also a need for a hybrid vehicle drive system that allows for the prevention of friction and wear by disengaging unused components. There is a further need for a hybrid vehicle drive system that uses regenerative braking to store energy in at least two rechargeable energy sources. Still further, there is a need for a PTO-based hybrid system. Further still, there is a need for a hybrid system optimized for use with a hydraulic system of the vehicle.
The need for engine idle reduction systems and methods also exists. Sophisticated power train control systems and power management systems required for the operation of a hybrid vehicle drive system can add cost and complexity. Therefore there is a need for an idle reduction system that allows equipment to be powered by one pump. There is also a need for a system that allows for quick recharging from three sources (vehicle engine, external power grid, APU). There is also a need for a system that can provide power to the equipment from two sources simultaneously (vehicle engine and electric motor) during periods when equipment power requirements exceed the output of only an electric motor driven pump.
There is a further need for a series/parallel design in which the system can operate using either series or parallel configurations depending upon which is most advantageous given operating requirements.